Basic Oracle Architecture question

Hello,

I am new to Oracle and I am confused over a couple of basic architecture issues.

(1) I have a multi-user application that connects to an Oracle
database. When I create Oracle users in DBA Studio, a schema is created for each of the users. So user U1 is looking at a different set of tables to user U2. But in my application I want each user of the application to be looking at the same set of tables! What is the usual way to handle this? Do I effectively have an "application" Oracle user, so each user of my application connects to the database as the same user (and therefore has the same permissions on the databas objects)?

(2) What exactly is a Schema? I have two Oracle books, neither of
which explain whether it is a logical concept (which I'm sure it must be), physical, or otherwise.

(3) I am aware that this question has been asked several times already
on Google, but unfortunately there are many conflicting answers (I am hoping to get a categorical answer from a real expert out there!) - My O'Reilly Oracle Essentials book states that "an instance can connect to one and only one database" but Kyte's book tells me that "a database may be mounted and opened by many instances. An instance may mount and open a single database at any point in time." I guess these statements are not necessarily contradictory. Assuming they are not conotradictory, could someone tell me how an instance points to a database, and how it can be changed to point to another database.

Many thanks,
Paul Received on Thu Dec 12 2002 - 17:31:16 CST